Pulverizing method and apparatus



May 27, 1958 F. c. MccoY 2,836,368

PULVERIZING METHOD AND APPARATUS Filed June 25, 1954 iiited tat@ rotvnnrznso Marriott) AND APPARATUS Application .lune 25, 1954, Serial No. 439,327

15 Claims. (Cl. 244-17) The present invention relates to a novel method and apparatus for pulverizing normally soft substances containing a liquid such as water which is characterized by the property of freezing to a solid material such as ice. More particularly, the invention also concerns the drying of substances so pulverized.

Brielly, the invention involves preparing line particles from 'relatively coarse particles of a substance which is impregnated with a freezable liquid, by first freezing the liquid content of the substance to a solid, thereafter pulverizing the brittle frozen coarse particles to form tine particles at a low temperature, and then passing the fine particles in heat exchange relationship with the coarse particles ahead of the freezing step to precool the coarse particles.

Among the substances which can be finely pulverized by my method are coarse particles of many foods containing natural water, such as potatoes, spinach, apples, fish, peas, and various meats. Other substances are coarse particles of such bibulous materials as sponge rubber, porous or spongy forms of cellulose, sawdust, tree bark, and foamed plastics such as polyvinylidene chloride, vinyl resins, styrene resins, and acrylate resins, all of which require artificial impregnation witha freezable liquid as by soaking in a pool to cause liquid to enter the pores of the substance.

After the frozen particles have been pulverized the content of water or other impregnating material is separated in any suitable way, as by melting and filtration, or by vacuum drying.

While the coarse particles can be passed through the freezing and pulverizng system in any suitable manner, l prefer to carry them suspended in either a gas such as air, or a liquid such as normal pentane which is immiscible with the freezable liquid and has a considerably lower freezing point.

For simplicity, in the following description the principles of the invention will be exemplified by the freezing of contained water to form ice in the particles to be pulverized. It is to be understood that other freezable liquids can also be used, such as tetrachloro diuoro ethane, l-bromo-l-chloro ethane, benzene, cyclohexane, and 1,4- dioxane.

Also, air will be described as the carrying gas, although other gases such as propane, nitrogen, argon or butane may be used.

Similarly, Where the particles are carried in slurry form by a liquid, pentane will be mentioned, although it is clear that other liquids can be used, such as higher paramn hydrocarbons (e. g., normal hexane), halogenated compounds such as ethylene dichloride, cycloparains such as methyl cyclopentane, and other nonreactive relatively low boilingand low melting compounds. The liquid used for slurry formation should have a relatively low boiling point in order that it might be separated from the ground material by vacuum vaporization, except where the ground material is Vnot affected by heating.

". as described in connection with Fig. l.

2,83%,358 Patented May 27, 1958 ice The principles of the invention will become more apparent from the following detailed description, having reference to the accompanying drawings, wherein:

Fig. l is a schematic liow diagram of apparatus for performing one modication of the invention, wherein the coarse particles are carried through the system by a gas;

Fig. 2 is a schematic flow diagram showing apparatus for performing a second embodiment of the invention wherein the coarse particles are suspended in a liquid for passage through the system; and

Fig. 3 is a schematic flow diagram showing apparatus for performing a third embodiment of the method of the invention, wherein a water-free bibulous material is iirst impregnated with water before passage through the pulverizing system.

Referring to Fig. l a water-saturated substance to be pulverized is sliced, torn, or otherwise reduced to a coarse average particle size such as 1/s-l/f. inch. The coarse particles are suspended in a flowing stream of a gas such as air by aspiration or another conventional manner, and are passed continuously through a conduit 11 into a precooler 13 wherein they are cooled to a low temperature above the freezing point of the occluded water, such as C., in a manner to be described more in detail hereinafter.

From the precooler the airborne particles iow through a conduit 15 into a freezer 17 wherein the occluded water is frozen to ice at a temperature of about C. by passing a suitable low temperature coolant through the freezer by way of an inlet conduit 19 and an outlet conduit 21. Spent coolant then ows through precooler 13 to precool the incoming particles. Suitable coolants are cold nitrogen gas or air evaporated from a liquid source, cold carbon dioxide gas evaporated from a solid block of carbon dioxide, cold brine, or a conventional evaporated refrigerant suchas ammonia, sulfur dioxide, or Freon.

The airborne frozen coarse particles then dow continuously in an unbonded discrete condition through a conduit 23 into a grinder 25 which may be of any conventional construction such as a roll mill, fluid energy mill, or hammer mill, wherein the brittle frozen particles and included ice are disintegrated to an extremely line condition. ice crystals assist in abrading the particles.

After pulverization the airborne cold pulverized partid cles and accompanying ice particles pass through a conduit 27 to precooler 13 to precool the incoming airborne feed. From precooler 13 the airborne pulverized particles pass by a conduit 29 into a vacuum dehydrator 31 wherein a high vacuum is maintained to cause the ice crystals to sublime and pass olf from the pulverized solid product particles, which then are removed in a dehydrated condition through an outlet 33.

in the modification shown in Fig. 2, coarse particle containing moisture are passed through a conduit 41 into a slurry tank 43 which is supplied with liquid pentane through a conduit 45, so that a slurry containing -65%, and preferably about solids by weight is formed. The slurry from tank 43 is pumped continuously by a pump 47 into a precooler 49 wherein its temperature is lowered to a point above freezing, such as 10 C., after which it passes through a conduit 5i into freezer 53 supplied with a coolant by a refrigerant system of conventional design. v

in freezer 53 the temperature of the slurry is lowered to a point such as 30 C. so that the water in the solid particles is frozen to ice while the pentane remains liquid to carry the frozen particles through a conduit 57 into a conventional grinder 59 wherein they are pulverized The resulting cold mixture of pulverized solid particles and accompanying ice particles suspended in coldV liquidrpenttmeV flows through a conduit 6l containing a pumped to the precooler 49 to lower the temperature ofthe incoming slurry.

From the precooler the.' slurry then passes by, a conduit 53 into a suitable separator' which removes most of the liquid pentane from the solid and other particles. Cold pentane is then `returned by a conduit66 to slurry tank 433. Separator 65 may be a ,conventional filter, centrifuge, or the like. i

The solid particles fare then transferred bya conduit 67 *toV a vacuum dehydrator 69 suchY as described in connection with Fig. `l, wherein water is removed together with any remainingV pentane, after whichrthe dry pulverized solid product is removed through an outlet 7i.

An alternativeoprocedure in operating the system of Fig. 2 is to close arvalve 68 and'ropen asecond valve 7i) Y so that ,the slurry flows intoa iilter or other liquid'separator V72.wherein all or Vpart of the liquid pentane is separated from the solids which then pass to freezer 53 through conduit '73. The separated liquid pentane flows through Y, aV conduit V74 tothe Vdischarge line 6l from grinder VSrl/here itmiaes with the dischargeto form a cold slurry iiowing as described previously.

Y in ,the modification shown in Fig. @coarse particles'V (say ,1/1-1/2 inch averagel diameter) Vof a dry, soft, resillent bibulous substance such as sponge VYrubber are introduced into a body of Water in a tank 75 wherein they absorb a substantial quantity of water.V The water soaked particles are then ,remoyed from tankjS, passed through a precooler 77, and intofa freezer 79 wherein their ternperatureJis reduced by ,a conventional'coolant. to freeze 'the absorbed water and embrittle the rubber,Y as described in connectionwith ligsl Vand 2.

From the freezer the coarse particles are passed into a conventional grinder .8l and pulverized to a iine condition. Ther resulting Ycold pulyerized product is passed by way of a conduit SZinto the precooler 77 and thence to a water separator 87 which may be asdescribed inconnection with Figs. l and 2, or may be constructed as aV device which melts ice and thereafter separates the water from the solid particles by filtration, centrifuging, decantation or the like. Cold water from the separator 87 flows nach to tank 8S as makeup througha line S8.:

An alternative Yprocedure in Voperating the systemV of Fig. 3 is to close a valve or gatej and'open a second valve or gate gi so that the :water soaked lumps pass Y to a filter or other Vwater separator 93 whereinV excess water is separated from the solids which then pass'into VYprecooier 77 through'a conduit `95.V The separated water flows througha conduit 97 4to the discharge line 82 from grinder Si where it mixes with't'ne cold discharge and is Y `cooled itselrpv to a Vlow temperature. A When a bibulous material -ispulverized as-described in connection with Vig thewater-soaked coarse particlesV may be conveyed through thelsystem in any suitable way, as on conveyor belts,-or by means of a gas or a waterimmiscible vliquid of4 low-freezing Vpoint such ,as pentane as described in Vcoitinection with Figs. l and 2.

Among the important advantages provided bythe ,method described aboveare'the economy` of operation which results from the transfer' of heat from incoming coarse solid particles'to loutgoing cold pulver-ized par` 'ticles.

Also, Vthe operation is rapid and continuous. Still other important advantages are that when the solid particles are suspended in a water-immiscible liquid, such as pentane, heat transfer to the coolant is highly*efficient,

and coherence of frozen particles together and adherlence of particles to the walls are prevented. Another important advantageris that substances which would Vbe clama'fed if'dehydrated by the application of heat, may

YVbe producedV undamaged in the dehydrated pulverized condition.

Gbviously, many modications and variations of the Yfassases, Y Y Y Y.

l invention, as hereinbefore set forth, maybe made with-` out departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

l claim:

l. A method for preparing tine particles from much l coarser particles of a substance impregnated with a liquid material characterized by the ability to freeze to a solid material, said method comprising freezing saidliquid material to solid, thereafter pulverizing said substance to form line particles at a low temperature, and passing said fine particlesin kheat exchange relationship with said coarse particles ahead of said freezing step to precoci said coarseV particles.

2. A method in accordance with claim l, also comprising separating said material from said -ine particles.

3. A method in accordance with claimV 2, wherein said material is separated by subjecting said particles to a vacuum.V r

4. A method in accordance with claimV 2, wherein saidV material is Separated by meltingi'said solid material back to liquid, and then removing said liquid from said particles. Y n

5. A method in accordance with claim 1V wherein excess liquid accompanies Vsaid coarserparticles, said method also comprising the Step of separating at least part of saidcXcesS liquid ahead of `said freezing step,

and passing separated liquid Ato the Vdischarge of said` pulverizing step. .v q :n

c 6. `A method for preparing Yline particles fromV much coarser particles of a substance impregnated with a liquid material characterized by theability to freeze to a solid,l Said methodV comprising suspending relatively coarse particles of said substance in a flowing stream 'of a gas, freezing said liquid material to a solid material while suspended insaid gas, thereafter `pulverizing said substance to form fine particles at a low'temperature and passing said finerparticles insuspension in said gas from the zone of pulverirzation into heat exchange relationship with said coarse particles yahead of said freezing step to precool said coarse particles. o Y

1 7. A method in accordance with claim 6,.also com- Y' prising separating said material from said fine particles. Y l .Y A

8. A method in accordance Withclaim l wherein said liquid materialY is frozen by passingin heat exchange re-V lationship withV SaidV particles a uid at a .temperature Y well below the freezing point of said liqlldmaterial, and Y subsequently passing'qsaidfluid in heat` exchange relationship with vsaidparticles ahead `of said freezing step for precoolingsaid particles Y g f 9. kA methodfor preparing yline particles from coarse particles of a substance impregnated with a rst liquid material characterized by the ability to freeze to l,a solid Vmaterial, said method comprising forming a slurry by suspending said coarse vparrticlesris` a second liquid` 'im miscible with said rst liquid material and characterized by having a freezing point lower thansaid lirst liquid material, cooling .said slurry to a temperature below the freezing point` of said rst Vliquid materialto freezek said first liquid material, thereafter; pulverizing said V substance in the presence of said V,second liquid to form a slurry of ypulverizedparticles Vin said second liquid, then be groundgameansl connecting said grinderto said` pre-k cooler t'onconveyingl coldcvground particles in heat exchangeY 'relationship with' coarse particles in 'said precooler; and drying means connected to said precooler for receiving and dehydrating said cold ground particles.

11. Apparatus in accordance with claim 10, also comprising means connecting said freezer with said precooler for conveying spent refrigerant to said precooler.

12. Apparatus in accordance with claim 10, wherein said means for dehydrating is a vacuum drier.

13. Apparatus in accordance with claim 10, also comprising slurry means for forming a slurry of coarse particles in a liquid to be passed through said precooler, freezer, and grinder; and a separator connected between said precooler and said drying means for separating said liquid from the ground particles before dehydration thereof.

14. Apparatus in accordance with claim 13, also comprising means connecting said separator with said slurry means to return separated liquid thereto.

15. Apparatus in accordance with claim 10, also cornprising means for irnpregnating coarse particles with a liquid to be frozen, said last-named means being connected to said precooler.

References Cited n the le of this patent UNITED STATES PATENTS 226,057 Gerner Mar. 30, 1880 953,946 Pinkler Apr. 5, 1910 2,347,464 Cono Apr. 25, 1944 2,418,746 Bartlett et al. Apr. 8, 1947 2,467,318 Kellogg Apr. 12, 1949 2,550,615 Stansbury Apr. 24, 1951 2,583,697 Hendry et al. Jan. 29, 1952 2,609,150 Bludau Sept. 2, 1952 

1. A METHOD FOR PREPARING FINE PARTICLES FROM MUCH COARSER PARTICLES OF A SUBSTANCE IMPREGNATED WITH A LIQUID MATERIAL CHARACTERIZED BY THE ABILITY TO FREEZE TO A SOLID MATERIAL, SAID METHOD COMPRISING FREEZING SAID LIQUID MATERIAL TO A SOLID, THEREAFTER PULVERIZING SAID SUBSTANCE TO FORM FINE PARTICLES AT A LOW TEMPERATURE, AND PASSING SAID FINE PARTICLES IN HEAT EXCHANGE RELATIONSHIP WITH SAID COARSE PARTICLES AHEAD OF SAID FREEZING STEP TO PERCOOL SAID COARSE PARTICLES. 